The present invention relates generally to methods of accessing main memory in a computer system. More particularly, the present invention relates to a page mode method of accessing main memory. Specifically, the present invention provides a method whereby a page mode memory access can occur despite an immediately previous idle cycle.
In high speed computer systems, main memory is used to store all information required by the current working set. It has been found that accessing main memory information in a page mode fashion can partially overcome the typical slow access speed of main memory. The reason for this is that a page mode access enjoys a shorter cycle time than a conventional memory access, thus allowing the memory system to more quickly respond to a CPU request.
There are specific limitations on the ability to make a page mode access at any given time. When a page mode access cannot occur, then a slower conventional access must be used. One of such limitations has been the requirement that the first main memory access cycle following one or more idle cycles be carried out via a conventional memory access. The reason for this has been that when an idle cycle occurs, the CPU is forced out of its pipelined addressing mode. In order to then again begin a series of memory accesses, a conventional access must first be forced. Forcing a conventional access at all times following an idle cycle in this manner causes the system to suffer a performance penalty.
Accordingly, it is a principal object of the present invention to provide an improved memory access method that generally overcomes the deficiencies of the prior art.
It is a more specific object of the present invention to provide a method whereby the first main memory access following one or more idle cycles may be carried out in a page mode fashion.
It is a related object to reduce the likelihood of a forced conventional access so as to improve system performance.